To determine the safety and possible effectiveness of memantinie, a drug which has been used for several years in Germany for the treatment of neurological disorder (such as Parkinson's disease), but has not been approved in the U.S. for any disease state. This study will look to see if memantine is helpful in curbing some of the effects seen with AIDS Dementia Complex, or ADC. ADC causes damage to the nervous system, particularly the brain and spinal cord.